Overview: Hypoplastic left heart syndrome (HLHS) is a spectrum of disease characterized by underdevelopment of the left ventricle with obstruction or atresia of ventricular inflow and outflow. HLHS accounts for approximately 2% to 3% of all cases of congenital heart disease, with a slight male predominance.1,2 Chromosomal abnormalities associated with HLHS include Turner syndrome, trisomy 13 and 18, and terminal 11q deletion.^1–3

Etiology and Pathophysiology: The structural defects of HLHS include varying degrees of hypoplasia of left heart structures including a hypoplastic ascending aorta and arch, aortic valve atresia or stenosis, hypoplastic left ventricle, mitral atresia or stenosis, and patent ductus arteriosus (PDA) and patent foramen ovale or atrial septal defect (ASD) (Fig. 75-1). In a majority of cases, the ventricular septum is intact, and in severe cases, thickening of the left ventricular endocardium or endocardial fibroelastosis is present.⁴ Coarctation of the aorta coexists in approximately 80% of patients.⁵ The right heart structures often are enlarged.⁵

Both the pulmonary and systemic circulations depend on the right ventricle. Oxygenated pulmonary venous blood returns to the left atrium, and because of the significant left ventricular inflow obstruction and decreased compliance, an obligatory left-to-right shunt is present at the atrial level, most often through a patent foramen ovale or ASD. In the right atrium, the oxygenated pulmonary venous blood mixes with deoxygenated systemic venous blood and flows into the right ventricle. Blood is pumped to the pulmonary artery, with systemic blood then flowing from right to left through the PDA. The brachiocephalic vessels and coronary arteries are perfused through retrograde flow from the PDA into the arch and ascending aorta. The descending aorta is perfused from antegrade flow through the PDA.

Clinical Presentation: Cyanosis and tachypnea generally are apparent within hours to 2 days after birth. Poor arteriovenous mixing as a result of inadequate interatrial communication can lead to early elevation of left atrial and pulmonary venous pressure, pulmonary edema, and right heart failure. Serious hemodynamic changes occur after the birth of an infant with HLHS when pulmonary vascular resistance begins to drop and the PDA begins to spontaneously close.⁶ When pulmonary vascular resistance drops, an increase in pulmonary blood flow and a decrease in systemic blood flow occur, leading to a decrease in systemic perfusion. When the PDA constricts, a further decrease in the ductal-dependent systemic and coronary circulations occurs, leading to a decrease in systemic perfusion, myocardial ischemia, shock, and death.

Imaging: HLHS is readily identified in utero. The condition is now discovered in approximately 60% of patients with use of prenatal echocardiography.7,8 Chest radiographic findings are variable. The heart may be normal in size or may be enlarged with a globular configuration, suggesting multichamber enlargement (e-Fig. 75-2). Pulmonary vascularity may be normal in the first hours of life, with a subsequent progressive increase in vascularity if no restriction to blood flow exists at the atrial level. Indistinctness of the pulmonary vessels or pulmonary venous congestion with interstitial lines or pleural fluid may be seen with a restrictive atrial septum.

Echocardiography is the imaging method of choice and generally delineates all relevant presurgical anatomy. Cross-sectional imaging can be performed as an adjunct to echocardiography in complex cases.⁹ Magnetic resonance imaging (MRI) may be especially useful when a marginally hypoplastic left ventricle is present and the possibility exists of a two-ventricle surgical repair (Fig. 75-3 and Video 75-1).⁴ In these cases, MRI can be used to assess the size of the left atrium, atrial septum, mitral valve orifice, left ventricle, and aortic root to help plan the most appropriate surgical repair. MRI increasingly is being used after the first stage of the palliative single ventricle surgery to reliably quantify the systemic right ventricle systolic function, tricuspid regurgitation, and residual or recurrent coarctation and for pulmonary artery stenosis or hypoplasia before the second-stage bidirectional cavopulmonary anastomosis.^10–12

Treatment: Initial medical management includes intravenous prostaglandin E₁ (PGE₁) to maintain ductal patency. Medical therapy, including ventilator adjustments, inhaled agents, and medications, is used to optimize the ratio of pulmonary to systemic blood flow and to minimize the volume load on the single functional ventricle to maintain adequate systemic perfusion.¹³

Surgical treatment consists of a staged reconstruction procedure (Fig. 75-4). The staged reconstruction involves three surgical procedures with the goal of creating separate pulmonary and systemic circulations supported by the right ventricle and accounts for the high neonatal pulmonary vascular resistance and the subsequent decrease in pulmonary vascular resistance. The first stage of the reconstruction—the Norwood procedure—often is performed in the first week of life.¹⁴ This procedure involves transection of the pulmonary trunk proximal to the pulmonary bifurcation and anastomosis of the pulmonary trunk to the aorta. A triangular patch of homograft material is used to augment the hypoplastic ascending aorta, aortic arch, and distal arch. The coronary arteries are then perfused retrograde through the small ascending aorta. The PDA is ligated. A complete atrial septectomy is performed. Blood flow to the lungs is reestablished via a modified Blalock-Taussig shunt (BT shunt) from the subclavian or brachiocephalic artery to the pulmonary artery. (Fig. 75-5). Alternatively, a right ventricle to pulmonary artery (RV-PA) conduit may be placed.¹⁵ The potential benefit of the RV-PA conduit is elimination of the diastolic runoff that occurs with a BT shunt. Diastolic runoff can lead to coronary and systemic artery blood flow steal or an increase in the ratio of pulmonary blood flow to systemic blood flow. The potential disadvantages of the RV-PA conduit include right ventricular dysfunction due to the ventriculotomy, the potential for aneurysm formation at the site of the conduit insertion, and right ventricular volume overload from pulmonary regurgitation because there is no valve in the conduit.^1,15

By approximately 3 to 6 months of age, pulmonary vascular resistance has physiologically dropped, and the second stage of the reconstruction—the bidirectional cavopulmonary (Glenn) anastomosis or hemi-Fontan procedure—is performed to redirect the upper body systemic venous return directly to the lungs. The bidirectional Glenn procedure involves anastomosing the superior vena cava (SVC) to the right pulmonary artery. The hemi-Fontan procedure involves anastomosing the pulmonary arteries to the superior caval-atrial junction and placing a patch into the superior aspect of the right atrium to isolate SVC return into the pulmonary arteries. At this time, the BT shunt is divided or the RV-PA conduit is obliterated and tricuspid valve repair and pulmonary artery angioplasty are performed, if necessary.

A “hybrid” approach, which combines surgical branch pulmonary artery banding to limit pulmonary blood flow with transcatheter ductal stenting to provide systemic flow, has more recently been advocated to achieve similar physiology to the stage I procedure without requiring cardiopulmonary bypass in the fragile neonate with HLHS (Fig. 75-6).^1,16 The comprehensive second-stage procedure then involves cardiopulmonary bypass, removal of the PDA stent and pulmonary artery bands, repair of the aortic arch and pulmonary arteries, division of the diminutive ascending aorta with reimplantation into the pulmonary root, main pulmonary artery to reconstructed aortic anastomosis, atrial septectomy, and a bidirectional Glenn or hemi-Fontan procedure.^1,16

The third stage of the reconstruction—the Fontan completion procedure—is generally performed at 18 to 36 months of age. This stage involves directing inferior vena cava blood flow to the pulmonary arteries either via an extracardiac conduit or an intracardiac right atrial baffle (lateral tunnel). If a patch was placed in the right atrium during the second stage of the repair, it is removed. This third stage achieves separation of the systemic and pulmonary circulations. A fenestration may be left in the Fontan circuit so if pressures become high, there can be a pop-off from the Fontan circuit into the heart, which may lead to a more stable postoperative course.17,18 Many fenestrations close spontaneously but also can be closed during a cardiac catheterization procedure.

Survival after the three-stage palliative procedure has improved steadily and now approaches 70%.⁸ The stage I Norwood procedure carries the highest mortality, ranging from 7% to 19%.¹⁵ Cardiac transplantation had been considered an alternative to staged Norwood palliation in the past, but because of limited donor availability and the recent improvement in survival following Norwood palliation, transplantation now generally is reserved for patients for whom staged palliation has failed.^1,19

Overview: Left ventricular outflow tract (LVOT) obstruction can occur at the level of the aortic valve or in the subvalvar or supravalvar regions. This spectrum of disease represents approximately 10% of cases of congenital heart disease.²⁰ Valvar aortic stenosis (AS) is by far the most common form of LVOT obstruction and has a male predominance of nearly 80%.²¹ Supravalvar AS accounts for 1% to 2% of AS in childhood and occurs spontaneously or may be familial, usually via autosomal dominant transmission. Up to 50% of patients with supravalvar AS have Williams syndrome. Subvalvar AS is slightly more common than supravalvar AS²²; it also has a male predominance and may be associated with more complex disease such as double-outlet right ventricle and transposition of the great arteries.

Etiology and Pathophysiology: Congenital aortic valve stenosis results from abnormal valve development rather than the degenerative disease commonly seen in adults. The stenotic valve has variable anatomy, with annular hypoplasia, thickened or tethered leaflets, and/or incompletely developed commissures. Valve morphology may predict clinical severity or associated disease.23,24 Whereas neonatal critical AS often is associated with a unicuspid valve and a small eccentric orifice, bicuspid morphology accounts for up to 95% of cases of congenital valvar AS and is present in up to 30% to 60% of patients with coarctation.^25,26 In addition to the abnormality of the bicuspid valve, the aortic root tissue is abnormal in these patients and can lead to significant aortic dilation above a stenotic bicuspid valve. The aortic dilation has been thought to be due to poststenotic dilation, but histologic abnormalities of the ascending aorta can occur without significant valvar stenosis or regurgitation. The histology is similar to the medial disease seen in persons with Marfan syndrome in addition to abnormalities of the smooth muscle, extracellular matrix, elastin, and collagen.^27,28

The narrowing in supravalvar AS most commonly is hourglass in shape, occurs immediately above the sinuses of Valsalva at the sinotubular junction, and may be associated with poststenotic dilatation of the aorta, diffuse aortic arch hypoplasia, aortic valve abnormalities, coronary artery ostial stenosis, or left ventricular hypertrophy.29,30 Supravalvar AS often is part of a widespread arteriopathy.

Subvalvar AS can be discrete or diffuse. The discrete form, which represents the majority of cases, is a thin fibromuscular diaphragm encircling the LVOT. In the more severe diffuse form, a fibromuscular subaortic band is present along the length of the LVOT, producing a tunnel-like narrowing. The fibrous process often extends to involve the aortic valve cusps or the anterior mitral valve leaflet. The more diffuse form usually is associated with other left heart lesions, including mitral stenosis, supramitral ring, parachute mitral valve, valvar AS, or coarctation of the aorta.³¹

Clinical Presentation: Severe or critical AS may be diagnosed prenatally or present early in infancy with severe left heart obstruction, congestive heart failure, dyspnea, and poor peripheral circulation. Systemic flow is ductal dependent in cases of critical AS. The clinical manifestations of AS in infancy depend on the degree of valvar obstruction, mitral insufficiency, left atrial hypertension, and left ventricular dysfunction, as well as the amount of shunted atrial and ductal flow and other associated left-sided obstructive lesions. In cases of severe obstruction, the left ventricle may be severely hypoplastic, dilated, or dysfunctional.

AS in children usually is the result of a bicuspid aortic valve, and the obstruction generally is not severe. The degree of ventricular obstruction progresses gradually with age. Children with mild to moderate AS generally are asymptomatic and usually present with a characteristic systolic ejection murmur. With more severe obstruction, symptoms include chest pain, dyspnea, decreased exercise tolerance, and syncope.

Hemodynamically, supravalvar AS mimics valvar AS. In the absence of Williams syndrome, cardiovascular symptoms are rare, but patients with supravalvar AS may experience left heart failure, dyspnea, angina, and syncope related to the degree of LVOT obstruction. Patients with peripheral systemic or pulmonary arterial stenoses may have associated left or right ventricular hypertension, respectively.

Subvalvar AS is generally progressive. The turbulent subaortic jet can cause shear stress on the aortic valve, leading to valve deformation and progressive insufficiency. Subvalvar AS is rarely detected in infancy but may be detected in childhood. Children may have an asymptomatic systolic ejection murmur. A diastolic murmur of aortic insufficiency may be found in older children as regurgitation increases with age. In older patients with moderate to severe obstruction, signs of left ventricular failure with dyspnea, chest pain, syncope, and tachypnea may occur.

Imaging: The chest radiograph in infants with critical AS shows cardiomegaly and pulmonary venous congestion. In older children with mild stenosis, the radiograph generally is normal. When moderate to severe stenosis and left ventricular hypertrophy are present, the cardiac apex is depressed toward the diaphragm and posteriorly to the inferior vena cava. Left atrial enlargement can be seen with severe stenosis. Poststenotic dilation of the ascending aorta is rare in young children (Fig. 75-7).

Echocardiography is the imaging procedure of choice for the evaluation of valvar AS. Cardiac MRI can be used to complement echocardiography in cases of poor acoustic windows or if larger field of view imaging is indicated. Goals of imaging include demonstration of the degree and location of obstruction, valve morphology, leaflet mobility and effective valve orifice area. Systolic valve area calculated by MRI planimetry correlates well with transesophageal echocardiography and cardiac catheterization measurements (Fig. 75-8 and Video 75-2).³² The valve typically appears thickened and doming, with asymmetric or restricted leaflet excursion. The gradient across the aortic valve in millimeters of mercury is calculated using the modified Bernoulli equation (4V², where V is peak Doppler velocity beyond the aortic valve in meters per second). Aortic valvular regurgitant fraction is calculated with phase-contrast MRI (e-Fig. 75-9). Evaluation of left ventricular size, systolic performance, and diastolic dysfunction is necessary. Assessment of aortic root, ascending aorta, and arch size is crucial in infants with critical AS. These patients may have abnormal endocardium, which can indicate the presence of endocardial fibroelastosis (e-Fig. 75-10). Surveillance of the thoracic aorta is indicated to evaluate for the development of aortic root dilation and aortic dissection associated with aortic valve disease (e-Fig. 75-11 and Video 75-3).²⁸

In supravalvar AS, imaging is tailored to evaluate for the presence of discrete or diffuse supravalvar narrowing of the ascending aorta, the coronary ostia, the degree of left ventricular hypertrophy, ventricular function, supravalvar pulmonary stenosis, and other sites of vasculopathy as clinically indicated (Fig. 75-12). In patients with subvalvar AS, evaluation for the discrete subaortic membrane or ridge and definition of the long subaortic area of the tunnel-type subaortic lesion is necessary (Fig. 75-13).

Treatment: Infants with severe or critical AS need urgent treatment. Patients are supported with a PGE₁ infusion to maintain ductal patency, mechanical ventilation, and inotropic medications. Urgent percutaneous balloon valvuloplasty is the treatment of choice. A neonatal Ross procedure (i.e., replacement of the aortic valve with a pulmonary valve annulus and trunk autograft, coronary reimplantation, and replacement of the pulmonary valve with a homograft conduit) has been advocated by some persons as the treatment of choice in patients with dysplastic valves or small aortic annuli33,34; however, increased mortality and higher rates of autograft deterioration in children compared with adults has resulted in less enthusiasm by others.^35,36 During the era of aggressive transcatheter intervention, early mortality for infants with severe or critical AS has fallen from as high as 43% to 4% to 13%.^37,38

Balloon valvotomy is considered in older children with a peak systolic ejection gradient of 50 mm Hg or greater at catheterization, for patients with angina, syncope, or congestive heart failure, and for persons who want to play competitive sports or become pregnant.39,40 Routine follow-up is necessary to evaluate for aortic insufficiency and recurrent stenosis. Late surgical valve repair or replacement is necessary in approximately 25% to 35% of patients.^38,41 For patients who require valve replacement, a bioprosthetic or mechanical valve may be placed or a Ross procedure may be performed.

Patients with AS are at increased risk for sudden death and endocarditis. The risk of sudden death is thought to significantly increase with symptoms⁴⁰ but probably has decreased in the era of aggressive and effective transcatheter treatment.⁴² The incidence of subacute bacterial endocarditis is rare but is approximately 35 times greater than in the general population and also increases with AS severity.^43,44

Indications for interventions related to supravalvar AS are less clear, but surgery is performed in symptomatic cases. The high likelihood of progression influences consideration for aortoplasty or LVOT reconstruction. Balloon angioplasty and stenting of associated pulmonary stenoses may be necessary. Complications include aortic aneurysms and infective endocarditis, and surgical mortality is low.⁴⁵ Given the recurrent and progressive nature of diffuse arteriopathy, long-term follow-up is warranted.

In asymptomatic patients, the timing of surgical intervention for subvalvar AS is controversial and is related to the degree and progression of LVOT obstruction and other associated heart disease.46–48 For persons with discrete subvalvar obstruction, fibromuscular resection with or without septal myectomy is performed, and operative mortality is low. Treatment for the tunnel-like narrowing form of obstruction varies, depending on the size and function of the aortic valve. The Konno procedure (i.e., aortoventriculoplasty, including replacement of the aortic valve) and modifications including valve repair or the Ross procedure (described earlier) may be performed (e-Fig. 75-14). A wide rage in the rates of recurrence and complications such as aortic regurgitation are reported; however, operative mortality, recurrence, and progressive AS are more common after repair of the diffuse type of subvalvar AS.

Overview: Coarctation of the aorta accounts for approximately 7% of cases of congenital heart disease,⁴⁹ with a male to female ratio of approximately 1.5 : 1.²⁸ Coarctation of the aorta is isolated or present with a PDA in 82% of cases.⁵⁰ A bicuspid aortic valve is seen in up to 30% to 60% of patients,^25,26,51 and ventricular septal defect (VSD) is seen in 11% of patients.⁵⁰ Other associated lesions include ASD, left-sided obstructive lesions, transposition of the great vessels, double-outlet right ventricle, and atrioventricular septal defect in 7% of patients.⁵⁰ Eleven percent to 15% of patients with Turner syndrome have aortic coarctation.^52,53 Berry aneurysms are seen in up to 10% of patients.⁵⁴ Coarctation of the aorta is seen in 15% of patients with PHACES syndrome (posterior fossa defects, hemangiomas, arterial anomalies, cardiac defects and coarctation, eye anomalies, and sternal defects or supraumbilical raphe).⁵⁵

Etiology and Pathophysiology: Coarctation of the aorta is a narrowing of the thoracic aorta that generally occurs adjacent to the insertion site of the ductus arteriosus just distal to the left subclavian artery. The coarctation is almost always juxtaductal and discrete, but varying degrees of tubular hypoplasia of the transverse arch and isthmus may be present and are more commonly seen in infancy.⁵⁶ The embryology of aortic coarctation is not known, but two theories have been proposed. One theory, called the ductal sling theory, suggests that an abnormal extension of contractile ductal tissue occurs circumferentially around the aortic lumen. Contraction of this tissue with ductal closure leads to a shelflike aortic narrowing in the juxtaductal region.⁵⁶ The second theory, called the flow theory, postulates that aortic coarctation develops as a result of decreased blood flow through the aortic isthmus as a result of left-sided obstructive lesions. In fetal life the aortic isthmus normally receives a relatively low volume of blood flow. Most of the flow to the descending aorta arises from the right ventricle through the PDA. The left ventricle supplies highly oxygenated blood to the ascending aorta and brachiocephalic vessels, with a small amount of flow going through the aortic valve. With left-sided obstructive lesions, decreased isthmic flow occurs, promoting abnormal isthmic development and leading to aortic coarctation.^56,57

The pathophysiology of coarctation of the aorta is related to the severity of the arch obstruction, the presence of collateral vessels, and associated cardiac lesions.⁵⁰ Initially, the neonate with coarctation will have a PDA, allowing blood flow to bypass the obstruction. With severe obstruction, left ventricular afterload is increased acutely following closure of the PDA, and patients then may present with congestive heart failure and shock. With less severe obstruction, collateral blood vessels develop to bypass the obstruction. The development of adequate collateral vessels may mask the presence of the coarctation until later in childhood or adulthood. Upper extremity hypertension is present in 90% of children and is thought to be secondary to three proposed mechanisms, including mechanical aortic obstruction, abnormal body baroreceptor settings proximal to the obstruction, and hyperactivation of the renin-angiotensin system caused by the underperfused kidneys.^50,58,59 Left-sided obstructive lesions may further increase left ventricular afterload, and the presence of a VSD may further increase left ventricular volume load, leading to pulmonary venous and arterial hypertension and heart failure.

Clinical Presentation: Infants with critical coarctation of the aorta, especially when it is associated with other cardiac defects, typically present by 7 to 14 days of life as the PDA begins to close and they have dramatic signs of congestive heart failure and poor systemic perfusion. Clinical symptoms include dyspnea, poor feeding, tachycardia, and signs of shock, including oliguria, anuria, and severe acidemia. Femoral pulses are weak or absent, and differential blood pressures generally show a gradient between the upper and lower limbs.⁵⁰

Coarctation of the aorta also may be diagnosed from infancy to adulthood in asymptomatic or mildly symptomatic patients, with a reported median age of 10 years (range, 1 to 36 years).⁶⁰ These patients present later because the coarctation is not significant or because adequate collateral circulation has developed. The diagnosis usually is made on the basis of routine physical examination findings such as an incidental murmur, hypertension, or absent or diminished lower extremity pulses.⁶⁰

Imaging: Infants with severe coarctation present with moderate to marked cardiomegaly and increased pulmonary vascular markings due to venous congestion from obstruction or overcirculation with an associated VSD (e-Fig. 75-15). Congestive heart failure presenting between the first and fourth weeks of life strongly suggests coarctation. Chest radiographs in children older than 1 year and younger than 5 years usually show a normal heart size, but cardiomegaly due to left ventricular hypertrophy can be seen. Rib notching as a result of dilated intercostal collateral arteries forming grooves on the rib undersurfaces is the hallmark of this condition and usually is seen after 5 years of age. The lower borders of the fourth through eighth ribs usually are involved posteriorly.⁶¹ The rib notching is bilateral unless an aberrant subclavian artery arising distal to the coarctation is present. Poststenotic dilation of the aorta below the coarctation usually occurs. A “figure three” sign frequently is seen along the left upper mediastinal border, related to the prominent aortic knob and left subclavian artery proximal to the coarctation, the indentation from the coarctation, and the poststenotic aortic segment below the coarctation (Fig. 75-16). The imprint of the aorta on the adjacent barium-filled esophagus, which is known as the “E” sign or “reversed three” sign, is caused by indentation of the esophagus by the dilated aorta proximal and distal to the coarctation.

Echocardiography is the method of choice for imaging coarctation in infancy. Computed tomography and MRI can provide detailed anatomic imaging of the coarctation in older children or adults with limited acoustic windows (Figs. 75-17 and 75-18). MRI also can be used to assess the hemodynamic significance of the coarctation. A complete imaging examination involves imaging for ventricular systolic function, volume and mass; atrioventricular and semilunar valve assessment with particular attention to the aortic valve; and imaging of the aortic root, ascending aorta, arch, coarctation, and descending aorta to the renal arteries. Maximum blood flow velocity, blood flow volume, and flow pattern in the aorta just distal to the coarctation can be assessed using phase-contrast MRI sequences (e-Fig. 75-19 and Video 75-4). The maximal flow velocity obtained across the coarctation can be used in the Bernoulli equation (see the previous aortic stenosis imaging section) to estimate the gradient across the coarctation.⁶² Aortic flow volume at the diaphragm also can be assessed using phase-contrast sequences. In patients with significant coarctation, the flow volume at the diaphragm may be increased relative to the volume just distal to the coarctation as a result of recruitment of collateral flow through the intercostal arteries and can be an indicator of the significance of the coarctation.^63–65

Treatment: Coarctation of the aorta that presents with congestive heart failure in the neonatal period is managed medically with inotropic drugs and PGE₁ to maintain ductal patency and improve blood flow to the descending aorta. After stabilization with medical therapy, urgent surgical repair is the treatment of choice.66,67 Balloon angioplasty can be considered as an initial procedure for neonates at high surgical risk.⁶⁶

Repair is performed on a more elective basis in patients who present in infancy or childhood with a murmur or upper extremity hypertension compared with critically ill neonates. Conventional therapy for aortic coarctation is surgical. Currently, the surgical procedure used most commonly in infants and children is resection of the coarctation with end-to-end or extended end-to-end anastomosis.50,66,67 Other surgical procedures, including patch aortoplasty and subclavian flap repair, are less commonly performed as the procedure of choice in children because of the risk of aneurysm formation at the patch site with patch aortoplasty and left arm complications and remnant residual ductal tissue with the subclavian flap repair.^50,66 The efficacy of balloon angioplasty for native aortic coarctation in infants and children has been a topic of controversy because aneurysm formation and iliofemoral artery injury are reported as being higher⁶⁸ and the reintervention rate for recurrent stenosis may be higher than for conventional surgical therapy.⁶⁶ Stent placement can be considered for primary coarctation repair in children who weigh more than 10 to 15 kg.⁶⁹ The transcatheter approach is accepted therapy for treatment of recoarctation in all age groups.⁶⁶ Late complications after surgical or endovascular treatment include recurrent coarctation, aneurysm or pseudoaneurysm formation, aortic dissection, and hypertension.^50,66,70

Overview: Interrupted aortic arch (IAA) is rare and accounts for approximately 1.5% of congenital heart anomalies.⁷¹ IAA consists of discontinuity between the ascending and descending aorta and is classified according to the location of the arch interruption.⁷² Type A interruption is the second most common type (seen in 42% of cases), occurs at the isthmus just beyond the origin of the left subclavian artery, and is seen in association with aortopulmonary window with an intact ventricular septum and with transposition of the great arteries and VSD.⁷³ Type B interruption is most common (seen in 58% of cases), occurs between the left common carotid and left subclavian arteries, and usually is associated with conotruncal abnormalities, large posterior malalignment VSDs, and subaortic stenosis.⁷³ Type B interruption is associated with aberrant origin of the right subclavian artery from the descending aorta.⁷⁴ DiGeorge syndrome is relatively common in patients with type B IAA and often is associated with a right aortic arch.⁷⁵ Type C interruption is least common (appearing in 4% of cases) and occurs between the right and left common carotid arteries. A PDA is seen in nearly all persons with IAA. Other lesions reported in association with IAA include isolated VSD (73%),⁷¹ ASD, bicommissural aortic valve, aortic stenosis, and more complex lesions including truncus arteriosus and the Taussig-Bing type of double-outlet right ventricle (see Chapter 76).⁷⁶

Etiology, Pathophysiology, and Clinical Presentation: The embryology of IAA depends on the type of interruption. Type A is formed as a result of abnormal distal fourth arch regression during late development, after the ascent of the left subclavian artery. Type B results from an early regression of the fourth arch before migration of the left subclavian artery. Type C likely results from abnormal regression of portions of the left third and fourth arches.

The pathophysiology of IAA is similar to other obstructive left heart lesions such as aortic coarctation. Patients are dependent on blood flow through the PDA. Once ductal closure begins, patients may present with profound systemic acidosis, anuria, and ischemic injury to the abdominal organs and lower extremities. If adequate collateral vasculature develops, the clinical presentation can be delayed.

Imaging: IAA may be diagnosed prenatally. Postnatal imaging is directed at defining the arch sidedness and branching pattern, the site of arch interruption, the size of the proximal and distal portions of the arch, the distance of interruption, the size of the aortic annulus, and the presence of a PDA (Fig. 75-20).⁷¹ Screening for other cardiovascular abnormalities also is performed. Echocardiography generally is sufficient for preoperative assessment. Cross-sectional imaging is obtained to better define arch branching or other cardiovascular anatomy as needed.

Treatment: PGE₁ infusion is begun upon patient presentation to keep the ductus arteriosus patent. Metabolic abnormalities are treated medically, and surgical repair is undertaken as soon as the infant is clinically stable.⁷¹

Complete surgical repair is performed in the neonatal period with generally good outcomes that depend on associated cardiovascular lesions.⁷⁶ Direct arch anastomosis between the ascending and descending aorta with ductal ligation is the preferred technique. Homograft, pericardial patch, or autologous carotid artery augmentation may be needed if the arch is hypoplastic.⁷⁶ An intervening conduit generally is not placed unless associated anomalies are present. Surgical technique modifications performed as a result of associated anomalies are based on individual patient anatomy.⁷¹

Postoperatively, monitoring for arch obstruction or dilation at the site of anastomosis is necessary. The incidence of postoperative arch obstruction is low, with a reported 74% actuarial freedom from arch obstruction necessitating reintervention at 15 years.⁷⁶ Assessment for complications related to other cardiovascular anomalies such as recurrent LVOT obstruction also is undertaken. Postoperative imaging generally is performed with echocardiography, with supplementary cross-sectional imaging as needed.